More specifically, the invention relates to a field effect transistor including:                a semiconducting substrate having two areas doped with electric charge carriers respectively forming a source area and a drain area;        a dielectric layer positioned above the semiconducting substrate between the source and the drain and forming the dielectric gate of the field effect transistor; and        a gate consisting of a reference electrode and of a conducting solution, the conducting solution being in contact with the gate dielectric.        
The invention also relates to a method for manufacturing such a field effect transistor.
Field effect transistors of this type are already known in the state of the art.
When a change in charges occurs at the surface of the gate dielectric, for example, when charged molecules or ions are positioned at the surface of the gate dielectric or by applying a gate voltage, the electric charge carriers present in the source and the drain are attracted into the semiconducting substrate under the gate dielectric by an electric field and may form a so-called conduction channel. A current then flows between the source and the drain. The transistor is then in a so-called conductive state. The width of the conduction channel and the intensity of the current which flows between the source and the drain depend on the charge present at the surface of the gate dielectric.
The most commonly encountered transistors in the state of the art have a gate dielectric formed with an inorganic material such as silicon dioxide (SiO2).
This type of transistor, although having interesting electric properties is not optimal for detecting charged biological molecules or ions in solution. On the other hand, the method for manufacturing this type of transistor comprises a step for thermal oxidation of silicon, which is often lengthy and which requires annealing in a temperature range which may extend up to 800° C.
In the state of the art, field effect transistors are also encountered which include a gate dielectric formed with an organic material. The main drawback of this type of transistor lies in the fact that the organic material layer forming the gate dielectric has a large thickness, which reduces the electric performances of the transistor. Indeed, the larger the thickness of the gate dielectric, the more the voltage to be applied to the gate for forming the conduction channel has to be high.
This type of transistor is therefore not optimal for detecting or studying biological molecules which do not support high voltages.